Basal Metabolic Rate (BMR)- overview

Basal Metabolic Rate – BMR

Globalrph student writer

Humans are burning calories every second without even knowing it. Whether you’re sitting, sleeping, or typing on a keyboard—your body is continually burning calories in order to have the energy to do its basic functions. The amount of energy at any given time is measured in kilojoules (KJ). This is also affected by your body’s metabolic rate. 

Basal Metabolic Rate (BMR) is the estimated energy expenditure per unit time a person needs to keep his body functions normal while at rest. It’s the amount of energy your body requires to maintain homeostasis. Some of these activities include a person’s change of breathing, blood circulation, cell growth, nutrient processing, and brain function. BMR is basically the number of calories that your body needs to survive at-rest state or simply your minimum rate of energy in order to keep yourself alive.

BMR is also known as RMR or the resting metabolic rate. It is the largest component of the total energy used. It takes up around 75% of an average person’s daily calorie burn and can be influenced by several factors including age, body mass, weight, height, and even gender. Studies found that men need more calories than women in order to survive.  

Measuring BMR can be tricky. Since a person’s BMR is never static, measuring the exact number can be a lot of work, especially if you don’t have the right equipment. BMR should be measured under a strict set of requirements including the physical and psychological state in a neutral environment. It should be done when a person is awake and requires the person’s sympathetic nervous system to be not stimulated. BMR is not always the same for each individual and a lot of variables can affect it. Knowing your BMR can help you understand how much calories you need to take in and reduce in order to lose weight.  

How To Calculate Your BMR 

There are several methods designed by scientists to calculate your BMR with the most accurate ones being performed in a lab. 

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The Harris-Benedict Formula 

The most common way of measuring BMR is through the Harris-Benedict Formula. First created in the early 20th century, the formula was revamped in 1984 and 1990. Today, this method remains the easiest out of all formulas. It can also be done without any medical equipment. The formula uses a person’s height, weight, age, and gender to calculate an average estimation of BMR. 

Formula for men:

BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)

Formula for women:

BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years) 

If you don’t want to compute manually, there are several online calculators using the
Harris-Benedict Formula you can use today. It can give you an estimation of the total number of calories you burn each day. Although this formula is easy, it’s also crucial to understand that it’s not 100% accurate. Getting a completely exact calculation of your BMR can only be done by an expert in a lab or a controlled testing environment. 

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The Katch McArdle Formula 

Another formula you can use is the Katch-McArdle formula which calculates your resting daily energy expenditure (RDEE). It differs from the Harris-Benedict through its calculation of lean body mass. This formula is often used by people who want to gain muscles so they can have their desired muscle and body fat percentage.

Here’s the Katch-McArdle formula for calculating BMR:

BMR = 370 + (9.7976 x LBM) kcal/day

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The Mifflin – St. Jeor Equation

Published in 1990, this equation is often called the update to the existing Harris Benedict-Method. The equation is more suited for the modern lifestyle which makes it the most accurate formula for calculating BMR estimates today. 

For men: 

BMR = (4.536 x weight in lbs) + (15.88 x height in inches) – (5 x age) +5 

For women: 

BMR (4.536 x weight in lbs) _ (15.88 x height in inches) – (5 x age) – 161

The importance of calculating your BMR is perhaps most beneficial to people who need to lose weight. Knowing the exact number of your BMR will enable you to understand how much calories your body needs. You can then proceed in setting a daily calorie limit for the food you consume each day. 

What Is Basal Metabolism? 

To understand basal metabolism, let’s first define metabolism. Metabolism is a biochemical process that includes everything that happens inside your body to keep you in optimal health. The rate at which a person burns calories or energy is called the metabolic rate. A person’s metabolic rate fluctuates based on activity level but the basal metabolic rate remains the same. 

Basal metabolism is the least amount of energy you need to survive during rest. It’s the number of calories your body burns while you’re in the rest state. It is often calculated to determine the energy needed for life support equipment to pump blood and maintain body temperature.

The Metabolism Process

The hypothalamus is the main organ responsible for regulating metabolism. It is a region on your forebrain which is also responsible for the coordination of both your autonomic nervous system and your pituitary. 

There are two parts of the metabolism process. The first one is called catabolism which is essentially the breakdown of food components into simpler forms. After they are transformed, your body uses them to create new cells or repair damaged ones. The second part of metabolism is called anabolism. This is the building or repairing process. If you eat more, the excess nutrients will be stored in your body as fat. 

Thyroid and Metabolic Rate

Your thyroid is important in your metabolic rate. The hormones produced by your thyroid are the ones that will determine how fast your body can burn calories. People who produce low metabolic hormones have hypothyroidism and can inhibit symptoms such as weight gain, dry skin, pale skin, and hair loss. 

What Factors Affect Metabolism?

Some people are naturally blessed with efficient metabolism which allows them to consume more food at any given time without any effect on their physique. Others have to be more careful in order to not put on excess weight. 

But how does metabolism vary from one person to another? Metabolism is determined by several factors such as sex, weight, age, and height. As you age, your body loses muscle mass and slows down metabolism. If you’re underweight and don’t consume enough calories to support your body’s needs, your metabolism slows down to 30 percent. Here are common factors that can affect your BMR:

Body Size, Gender, and Ethnicity

Basal metabolism can also be affected by a person’s body size, gender, and ethnicity. The taller and heavier you are, the higher your metabolic rate will be. However, if you have more fat tissue than muscle tissue, you’ll have lower metabolic activity and as your lean muscle mass increases, your metabolic rate does too. Generally, men have a higher metabolism than women because men have more muscle mass than women of the same size. 

Age

As people age, they lose a significant percentage of their lean muscles which means they’ll have a slower metabolism. In order to keep their body functioning properly, they have to make efforts to eat healthier. Children, on the other hand, have double the amount of an old person’s metabolic person. This is due to the rapid synthesis of cellular materials and the growth of their body. Studies suggest that children’s metabolism peaks at ten years of age. 

Body Fat 

The amount of body fat a person has can also influence their metabolism. Fat cells burn fewer kilojoules than other tissues or organs. 

Fasting

Starving or fasting can slow down metabolism to conserve energy. Whenever you restrict your body with calories, your body goes on conservation mode to store whatever it can. To have a stable metabolism, aim for a consistent and balanced diet. 

Genetics

Others have a higher metabolic rate because of their genes. Some people also have severely low metabolism because of certain genetic disorders. For example, people with fructose intolerance have the inability to break down fructose from fruits, sugar, and vegetables. People with phenylketonuria can’t convert the amino acid phenylalanine into tyrosine which in abundance can cause brain damage. 

Hormonal Factors 

Hormonal imbalance such as hypo hyperthyroidism can also affect one’s metabolism. Physiological conditions that change hormones such as pregnancy and lactation can also affect metabolism.

Drugs, Beverages, and Stress Levels 

Certain drugs such as nicotine and caffeine found in beverages can also increase your metabolic rate. Your state of mind is also a factor that can affect your energy expenditure and your metabolic rate. 

Environmental Temperature

Very low or very high temperatures can increase metabolism since your body exerts more energy to maintain normal body temperature. This is also the reason why people who live in tropical climates have generally 5 to 20 percent higher metabolic rate than those people who live in more temperate areas. 

Physical Activity 

The more active you are and the more muscles you have, the more calories you’ll burn. When you exercise regularly, you also teach your body to burn kilojoules at a faster rate. This is why exercising consistently helps keep you from gaining weight. 

How Does The Body Burn Energy? 

The human body burns energy in three main ways: basal metabolism, thermogenesis activity, and thermic effect of food. 

Basal Metabolism – The body burns around 60 – 75% of calories in the basal metabolism state. This means that during rest is when your body burns the most fat. Most people aren’t aware of this. 

Thermogenesis – The body burns around 15 – 30% of calories through thermogenesis activity or movement and exercise. A moderately active person who exercises for around 30 minutes a day can burn 20 percent of his stored fuel. During heavy physical activity, a person’s muscles can burn up to 3,000 KJ per hour. Here are examples of activities and the approximate amount of energy used per hour of doing them. 

• Rowing – 67
• Running – 29.3
• Walking Rapidly – 14.2
• Driving a car – 3.8 
• Standing – 2.1
• Sitting – 1.7

Thermic Effect of Food – The body burns around 10% of calories during digestion.  Each type of food can also raise BMR differently. For example, fats can raise your BMR from 0-5 percent. Carbohydrates can raise your BMR to 5-10 percent, and protein to around 20-30 percent. Spicy food also has an extra thermic effect. 

How To Raise Your BMR?

Many people think that metabolism is something you can control and “speed up”. And although there are foods and supplements that may temporarily speed up your metabolic rate, it’s too short that it wouldn’t have any effect on your body. 

Build Muscle 

According to scientists, the best way to raise your BMR is to improve your body composition or in short: by building more muscles. The harder you workout, the more muscle you build, and the more muscles you have, the more calories you’ll burn. A person with lots of lean muscles can have a higher metabolic rate. This is because muscles use more energy than fat while at rest which means it can quickly burn stored fuel. Strength training workouts mixed with cardiovascular activities such as running or swimming can give you the best results. Regular exercise can also increase your calorie burn even after days of workout. 

Best Activities For Burning Calories 

• Aerobic exercises – 150 minutes of aerobic activity per week can make you burn calories faster. To make this doable, you can set a schedule of 30 minutes a day of aerobic exercises. Examples of these exercises include cycling, swimming, or brisk walking. 
• Strength Training – Increasing your muscle mass can help you burn more calories. Muscle-training can be done for 30 minutes for 2-3 days a week.
• Even simple activities that help you get extra movement such as taking the stairs instead of using the elevator can go a long way. Other house chores such as washing your car, gardening, and washing dishes can also contribute to faster calorie burning.

Eat a Balanced Diet 

Cutting on calories and trying different kinds of crash diets won’t do you any good. The best way to boost your metabolism is to practice a healthy diet of whole, unprocessed food. The quality of your diet can fuel your body and boost your metabolism in the long run. So make sure you’re paying close attention to the food you eat.

Stay Hydrated and Have Enough Sleep 

Proper hydration is important for the optimal function of your muscles and organs. Drinking plenty of cold water can also temporarily raise your metabolism. Getting enough sleep every night will also reward you with a faster metabolic rate. Study after study shows how sleep deprivation affects your internal processes.